I. Field of the Invention
The present invention relates generally to power riding trowels for finishing concrete that are equipped with manual steering. More particularly, the present invention relates to motor powered riding trowels of the type classified in United States Patent Class 404, Subclass 112, and to manual steering levers and linkages associated with such trowels.
II. Description of the Prior Art
It has long been recognized by those skilled in the art that freshly placed concrete must be appropriately finished. Proper and timely finishing insures that desired surface characteristics including appropriate smoothness and flatness are achieved. Motorized riding trowels are ideal for finishing large areas of plastic concrete quickly and efficiently, and such trowels have become a standard in the industry.
A typical power riding trowel comprises two or more bladed rotors that project downwardly from the frame and frictionally contact the concrete surface below for finishing. The rotors are driven by one or more motors mounted on the frame. Typically the motors drive suitable reduction gearboxes (i.e., 20:1 reduction) to power the twin rotors. The riding trowel operator sits on top of the frame and controls trowel movement with a steering system that tilts the axis of rotation of the gearboxes and the rotors. The weight of the trowel is transmitted frictionally to the concrete by the revolving blades. The unbalanced frictional forces caused by rotor tilting facilitate various trowel displacements, ultimately enabling steering and propulsion.
In a typical twin rotor design, each of the twin gearboxes has an axis of rotation that is generally perpendicular to the concrete surface over which the trowel moves. Each axis of rotation occupies a so-called “biaxial” plane that is perpendicular to the concrete surface. For steering and propulsion, both rotors are tilted by the steering linkage. Normally, twin vertically oriented steering levers in front of the seated operator are used to control steering. These steering levers run a pair of parallel, tilting levers beneath the trowel frame that tilt the gearboxes for steering. As explained in the numerous prior art references below, when the rotors are tilted such that they move in an arc that is coincident with or parallel to the biaxial plane, trowel weight is concentrated generally on the left or right periphery of the various rotors (i.e., the finishing blades) contacting the concrete, and the trowel moves forwardly or backwardly, or it can rotate, etc. To move left or right, at least one of the gearboxes is tilted through an arc that is generally perpendicular to the biaxial plane, concentrating weight on the front or rear periphery of at least one rotor, moving the trowel left or right.
Holz, in U.S. Pat. No. 4,046,484 shows a pioneer, twin rotor, self propelled riding trowel with manual steering. U.S. Pat. No. 3,936,212, also issued to Holz, shows a three rotor riding trowel powered by a single motor. The designs depicted in the latter two Holz patents were pioneers in the riding trowel art.
Prior U.S. Pat. No. 5,108,220 owned by Allen Engineering Corporation, the same assignee as in this case, relates to an improved manually steered riding trowel. Its steering system enhances riding trowel maneuverability and control. The latter fast steering riding trowel is also the subject of U.S. Pat. No. Des. 323,510 owned by Allen Engineering Corporation.
U.S. Pat. No. 5,613,801 issued Mar. 25, 1997 to Allen Engineering Corporation discloses a power riding trowel equipped with twin motors. The latter design employs a separate motor to power each rotor. Steering is accomplished with structure similar to that depicted in U.S. Pat. No. 5,108,220 previously discussed.
Allen U.S. Pat. No. 5,480,257 depicts a twin engine powered riding trowel whose guard structure is equipped with an obstruction clearance system. When troweling areas characterized by projecting hazards such as pipes or ducts, or when it is necessary to trowel hard-to-reach areas adjacent walls or the like, the guard clearance structure may be retracted to apply the blades closer to the target region.
Allen U.S. Pat. No. 5,685,667 depicts a twin engine riding trowel using “contra rotation.” For enhanced stability and steering, the rotors rotate in a direction opposite from that normally expected in the art.
U. S. Pat. No. 5,967,696 Oct. 19, 1999 issued to Allen Engineering Corporation depicts a CVT riding trowel, i.e., a trowel with a variable ratio transmission.
Recent patents pertaining to manually steered, dual rotor powered riding trowels include U.S. Pat. Nos. 7,775,740, 8,132,983, and 8,511,934.
With modern power steering designs, the rotors are tilted hydraulically with sophisticated control circuitry that ultimately tilts the rotors for trowel movements as described above. Although hydraulically steered riding trowels may be preferred for many applications, the earlier-developed manually steered riding trowels remain popular. This invention is primarily concerned with manually steered trowels utilizing front levers for steering control.
Relative to hydraulically steered and/or powered trowels, manually steered riding trowels have many advantages, including reduced cost, less complexity, lower weight, higher reliability, and ease of service. Most manually steered trowels position a pair of generally vertically upright primary control steering levers or bars in front of the seated operator. The steering levers have handles grasped by the operator. Each steering lever controls a lower, tilting lever arm extending beneath the frame in a direction generally perpendicular to the biaxial plane. When the primary steering control levers are pulled or pushed, the rotors are tilted to displace the trowel forwardly or backwardly. In most designs, both steering levers may be displaced forwardly or backwardly by pushing or pulling. Commonly at least one of the steering levers may be tilted sideways to produce left or right trowel movements.
With many manually steered trowels, including most prior Allen trowel designs, only one of the steering levers is displaceable sideways, although both can be pushed or pulled. On the other hand, with many competitive manually steered trowel designs, both of the steering levers are movable sideways back and forth. Thus, in the concrete finishing arts, there are two basic riding trowel steering genres. Experienced trowel operators can become accustomed to steering with sideways movements of just one steering lever (i.e., with Allen units), or, alternatively, with sideways movements of both levers.
Most trowel operators prefer the steering characteristics of the type of trowel they first encountered and learned.
Thus it has become apparent to me that manually steered riding trowels should be transformable between the two types of steering characteristics discussed above. Thus when a potential purchaser considers replacing an older, manually steered trowel, a new trowel constructed in accordance with the invention can be easily switched to the desired steering genre, satisfying the preferences of the customer. The transformable steering of the instant invention allows an experienced trowel operator to select the same steering “feel” that he or she has grown to prefer.